1. Technical Field
The present disclosure relates to a power transmission device and a wireless power transmission system which are used for wireless power transmission by which non-contact transmission of power is performed.
2. Description of the Related Art
In recent years, movable devices which can be charged, such as portable information terminals and electric vehicles, have become widespread. A wireless power transmission system for such devices is being developed. As the wireless power transmission technology, schemes such as an electromagnetic induction scheme, a magnetic field resonance scheme (a resonance magnetic field coupling scheme), and an electric field coupling scheme are known.
The wireless power transmission system of the electromagnetic induction scheme and the wireless power transmission system of the magnetic field resonance scheme include a power transmission device provided with a power transmission coil and a power receiving device provided with a power receiving coil. The power receiving coil complements the magnetic field generated by the power transmission coil, whereby it is possible to transmit power without bringing electrodes into direct contact with each other.
One of the requirements which are required in wireless power transmission is to make it unnecessary to perform positioning between the power transmission device and the power receiving device. That is, the requirement is that it is possible to perform high-efficiency power transmission without adjusting the position and orientation of the power receiving device to particular position and orientation. For example, as depicted in FIGS. 1A and 1B, even when the relative position of a power receiving device 200 with respect to a power transmission device 100 varies, the power transmission efficiency which is maintained so as to be roughly constant is required. One of the technologies that eliminate such positioning is a method called a coil array type.
In the coil array type, a power transmission device has a coil array formed of power transmission coils, and a power transmission coil to which power is applied is selected according the position of a power receiving coil. As a result, irrespective of the position of the power receiving coil, it is possible to perform high-efficiency power transmission. A wireless power transmission system of such a coil array type is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2012-504844, U.S. Pat. No. 8,519,668, and U.S. Pat. No. 8,629,654.